I read a lot of post about ppl getting upset about being "low-balled". I'm wondering if there is a different definition than the one I know. "Making a low offer"!
I do low-ball on larger items. And can you really get upset when you post a 10 year old 20 gal tank for $100 and someone "low-balls" you? I have and probably will do again and again in my life, it's called haggling.
The "I've only got $x money with me" is an age old line. I don't think is wrong when it is done as part of the haggling. Agreeing on a price and then pulling it after the fact is just not cool.
As my wife is "de-junking" the house again -- my big one is people who go hunting for free stuff to re-sell and make a buck. If I'm giving something away for free, it's because I don't care about the little bit it is worth and would rather see more people enjoying the hobby.
For both me and the wife, the trick we find works is this -- TRADE the item for something common in the hobby (almost worthless) for what you were giving away free. I did trade a 3 year old 90 gal for a SPS frag a few years ago

I honestly was giving it away, but the frag shows he at least has an interest. My wife usually asks a stupid low price for things she is giving away as it avoids the "FREE" label, and then just lets them have it for free when they show.
Around Kamloops there seems to be quite a few that spend all day hunting for free stuff people are giving away -- to re-sell and make a few bucks. I sell/give away any older salt water gear to be nice and promote reef tanks, not so some putz that doesn't even know what it is other than he can sell it on ebay.